1. Field of the Invention
Novel derivatives of dicyclohexylcarbodiimides, their process of synthesis and their use in synthesizing oxizine, diazine and thiazine leuco dyes are described.
2. Background of the Art
Leuco dyes are compounds which have found increasing importance in color imaging processes. These leuco dyes tend to be colorless until they are oxidized and then they form a visible color. It is required that these leuco dyes be reactive with moderate oxidizing conditions and yet not be so reactive as to form colors from mere environmental conditions. There are many different chemical classes of leuco dyes known to the imaging chemist.
Oxazine, diazine and thiazine leuco dyes are known to the imaging chemist as shown in Japanese Pat. No. 47-4638, U.S. Pat. No. 3,873,340, and U.S. Pat. No. 3,447,944. One particular class of these azine dyes that has found particular utility in oxidative color imaging processes is the 4-aryloyl derivatives. These azines display a good balance of reactivity and stability and the resultant dyes are also stable.
The typical synthetic procedure for the 4-aryloyl azine dyes involves the acid chloride derivitization of the aromatic acid (e.g., benzoic acid) and its subsequent reaction with an azine to form the appropriately substituted azine leuco dye. This procedure produced useful yields and dyes of pure quality, but in the case of a 3,5-di-tert-butyl hydroxy-substituted benzoic acid the yields were undesirably low because of polymerization of the acid chloride intermediates. The polymerized moieties can be separated from the leuco dyes, but that portion of the intermediate was lost in the production of the leuco dyes.